Transfer boxes are integral components in four-wheel drive and all-wheel drive vehicles, situated between the transmission and front/rear drive axles. They split torque from the transmission and distribute it to multiple axles, enabling selectable or automatic drive modes – 2WD, 4WD High, and 4WD Low. Internal gearsets, including bevel and spur gears, provide the necessary reduction ratios for low-range operation and differing wheel speeds. Many units incorporate a viscous coupling or multi-plate clutch for automatic torque distribution between axles. Robust housings, typically cast aluminum or iron, withstand high torsional loads and off-road conditions, and input/output shafts utilize standardized splines for compatibility.